This invention relates to a sheet-driven type automatic drafting machine provided primarily with a drive roller, a press roller, and a line-drafting head, in which a paper sheet is nipped by these two rollers and then the sheet is sent along an X axis direction during a rotation of the drive roller, and the line-drafting head moves along a Y axis direction, in order to draft the desired drawing on the paper sheet on a sheet mounting member.
Conventionally, in a conventional sheet-driven type automatic drafting machine, the horizontal distance between two press rollers has been determined disadvantageously manually by an operator according to the width of the sheet of paper used so as to place both press rollers at both side portions of the sheet of paper.
In consequence, it is the first purpose of the present invention to provide a sheet-driven type automatic drafting machine provided with two press rollers, in which the horizontal distance between the two is automatically controlled.
According to a press roller supporting mechanism of the conventional sheet-driven type automatic drafting machine, a press roller arm 2 is supported so as to oscillate around a shaft 4 and is urged clockwise as shown in FIGS. 12A and 12B by means of a tension spring 6. Thus, the press roller 8 is resiliently pressed against the drive roller 10 due to the resilient force of the tension spring 6. When the press roller 8 is raised from the drive roller 10 so as to permit insertion of a sheet between the drive roller 10 and the press roller 8, an eccentric cam 12 rotates to a position at which a long radius or enlarged portion 12a of the eccentric cam 12 presses the press roller arm 2 at an arm portion between the tension spring 6 and the shaft 4 downwardly against the resilient force of the spring 6. Owing to the downward pressing force of the eccentric cam 12, the press roller arm 2 oscillates counterclockwise around the shaft 4 and as a result the roller 8 is separated from the drive roller 10 as shown in FIG. 12B.
According to the conventional construction of the press roller supporting mechanism, a large friction force is generated between the press roller arm 2 and the eccentric cam 12 due to the force of the tension spring 6 before the press roller rises. In consequence, when it is intended to move these press rollers to the most suitable positions according to the sheet size, a large load or force is needed to control and move the press roller arm 2 provided with a press roller 8, and the press roller arm fails to move smoothly. In this situation, it has been necessary to move and control the press roller arm exclusively by hand.
In consequence, it is another purpose of the present invention to provide a sheet-driven type automatic drafting machine have press roller arms which can be moved with light force, so that it is possible to control and move the press roller arm automatically.